You have to lay 3miles of pavement, 5 feet wide, bricks are 5x10 inches. How many bricks to buy? You have 4 square mile of land with dense forest. Trees grow 5

You have to lay 3miles of pavement, 5 feet wide, bricks are 5x10 inches. How many bricks to buy? You have 4 square mile of land with dense forest. Trees grow 5 feet apart and are 10 inches thick on average. How many trees are there? How much wood can you expect? There's 5 inches of snow on your 5000 square feet roof. How much does it weight? Can it break the roof? Should you clean it up or can it stay? These things are mental-math in metric and notebook-math in imperial, and that sucks. Of course you can work around that. People always avoid the bad parts of the tools they use and find workarounds. Like not using exceptions in C++ or comparisons in javascript. If it's a widely used tool you know it has to work somehow. Thus Americans never convert between units unless absolutely necessary and write press articles like "Asteroid the size of 3 elephants missed Earth by 1000 football stadiums" :) But let's not pretend it's not a problem.